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How to Migrate Oracle Stored Procedures and Functions to PostgreSQL

Oracle offers PL/SQL coding features such as packages, stored procedures, functions and triggers to implement the logic of data management inside a database. PostgreSQL similar capabilities for the database logic with some differences in syntax and semantics that require attention during conversion between those two DBMS. Unlike data transfer, migration of stored procedures, functions, and triggers from Oracle to PostgreSQL is a complex task that requires careful consideration and planning. In this article, we will explore some tips and tricks to help database engineers or other responsible staff migrate source code from Oracle to PostgreSQL.

When migrating from Oracle to PostgreSQL, it is essential to understand that Oracle uses packages to organize functions into semantic groups, whereas PostgreSQL uses schemas for the same purpose. Additionally, there are no package-level variables in PostgreSQL, but they can be emulated as data of a temporary service table. To ensure a successful migration, it is crucial to research the best practices for translating stored procedures from Oracle to PostgreSQL functions to understand both systems and the problems that each procedure/function solves, instead of simply converting the syntax.

Moreover, besides syntax differences, it is essential to have a good understanding of both Oracle and PostgreSQL before beginning the migration process. If your application uses proprietary features of Oracle, you will need to rewrite those parts of the application that use Oracle. It is essential to address any differences in syntax and functionality between the two systems to ensure a smooth transition.

Below is the partial list of most important differences between Oracle and PostgreSQL:

  1. PostgreSQL requires all subselects have aliases while in Oracle it does not need a name
  2. Oracle does not distinguish NULL and empty string that must be point of special attention to preserve proper semantics in the migrated code in PostgreSQL
  3. Oracle may use special syntax for outer join using operator (+). It has to be translated into SQL standard syntax when migrating to PostgreSQL
  4. Oracle and PostgreSQL treat sequences in a different way. The following Oracle method to produce the next value mysequence.NEXTVAL must be converted into PostgreSQL equivalent nextval(‘mysequence’)
  5. Oracle supports specific statement DECODE that must be replaced by CASE/WHEN in PostgreSQL code
  6. PostgreSQL treats body of stored procedures and functions as a string, so it must be enclosed in the dollar-quotes $$. Also, the DBMS requires ‘LANGUAGE’ specification at the end of body.
  7. Create statements of Oracle triggers include source code right in CREATE TRIGGER declaration. PostgreSQL requires that source code of trigger is arranged as standalone function with reference from CREATE TRIGGER declaration.

To simplify the migration process, it is possible to use special tools that can partially automate the migration of stored procedures, functions, triggers, and views from Oracle to PostgreSQL. One such tool is the Oracle to PostgreSQL Code Converter developed by Intelligent Converters. This tool can migrate stored procedures, functions, triggers, and views, and convert Oracle built-in functions into PostgreSQL equivalents. Predefined Oracle types are mapped into PostgreSQL, and reserved words and identifiers are handled intelligently. The source code can be extracted directly from the database or from a PL/SQL script file.

However, it is important to note that although the Oracle to PostgreSQL Code Converter automates the migration of basic syntax patterns and constructions, some manual post-processing of the output code may be required, especially for large and complicated fragments of the source code. Therefore, it is essential to test the migrated code thoroughly to ensure that it operates correctly.

You can learn more about Oracle to PostgreSQL Code Converter on the official site of Intelligent Converters.